If proponents of Hubbert peak theory are correct, world oil production will at some point peak, if it has not done so already. Regardless, world energy consumption continues to rise at a rate that outpaces new oil discoveries. As a result, alternative sources of energy must be developed, as well as new technologies for maximizing the production and efficient consumption of oil.
In maximizing the production of oil, deepwater and permafrost drilling are being developed because they allow for production of oil and gas in reservoirs that have previously been inaccessible. Deepwater drilling is the process of oil and gas exploration and production in depths of more than 500 feet. Permafrost drilling is the process of oil and gas exploration and production in areas where seasonal temperatures are cold enough for permafrost to exist. Both had been economically infeasible for many years, but with rising oil prices, more companies are now routinely investing in these areas.
In addition to conventional oil and gas development, attractive alternative sources of energy may be developed. One potentially very large alternative source of energy is marine and permafrost natural gas sequestered in materials called clathrates. A clathrate is a chemical compound in which molecules of one material (the “host”) form a solid lattice that encloses molecules of one or more other materials (the “guest(s)”). Clathrates are also called inclusion compounds and important features of clathrates are that not all the lattice cells are required to be filled (i.e. they are non-stoichiometric) and the guest molecule(s) are not chemically bound to the host lattice.
Naturally-occurring clathrates of natural gas form when water ‘host’ molecules and certain low molecular weight hydrocarbon gas ‘guest’ molecules are brought together under suitable conditions of relatively high pressure and relatively low temperature. Under these conditions the “host” water molecules will form a cage or lattice structure capturing one or more hydrocarbon “guest” gas molecules inside. Large quantities of hydrocarbon gas are closely packed together by this mechanism. For example a cubic meter of natural gas hydrate contains approximately 0.8 cubic meters of water and generally 164 cubic meters of natural gas at standard temperature and pressure conditions.
Methane is the most common guest molecule in naturally-occurring clathrates of natural gas. Many other low molecular weight gases also form hydrates, including hydrocarbon gases such as ethane and propane and non-hydrocarbon gases such as CO2 and H2S.
Natural gas hydrates form naturally and are widely found at about 200 meters depth below the surface in permafrost areas, potentially within and below the permafrost layer. Natural gas hydrates also are found in sediments along continental margins at water depths generally greater than 500 meters (1600 feet) at mid to low latitudes and greater than 150-200 meters (500-650 feet) at high latitudes. The thickness of the hydrate stability zone varies with temperature, pressure, composition and availability of the hydrate-forming gas, underlying geologic conditions, water depth, salinity, and other factors.
Estimates of the amount of methane sequestered globally in natural gas hydrates have varied widely. The earliest estimates ranged between 100,000 and 100,000,000 trillion cubic feet (TCF). Since the start of dedicated drilling in the mid-1990s researchers learned that the percentage of natural gas hydrates within the pore spaces of marine sediments (referred to as natural gas hydrate saturation) were often far lower than the theoretical maximum saturation. This led to downward revisions of the amount of methane sequestered globally in natural gas hydrates to between 100,000 and 5,000,000 TCF with the most frequently quoted estimate of 700,000 TCF (a number which excludes any hydrates located in Antarctic or alpine permafrost areas). Even the lowest estimate represents an enormous potential new energy resource, equal to more than 4,000 times the amount of natural gas consumed in the US in or 18 times the entire world's proven gas resources.
Recognizing that only a fraction of the globally sequestered methane is likely to be concentrated enough and accessible enough to be produced, and acknowledging that to date there has never been a long-term production test of natural gas hydrates, it is still clear that natural gas hydrates have the potential to become a very large new energy source for the world.
To produce gas from natural gas hydrates the natural gas hydrates must first be converted back (“dissociated”) into water (either liquid or ice) and producible free gas molecules by one or any combination of four methods:                Addition of heat until the natural gas hydrate is outside the phase stability envelope        Reduction of pressure (depressurization) until the natural gas hydrate is outside the phase stability envelope        Addition of a hydrate inhibitor such as a salt, methanol, etc. to shift the phase stability envelope to the point where the natural gas hydrate is outside the phase stability envelope        Molecular substitution, where one type of guest molecule is substituted for another        
Although only a few natural gas hydrate production tests have taken place, all of very limited duration, significant work with reservoir simulators and laboratory experiments have led those experienced in the art to generally believe that depressurization would the most economical form of natural gas hydrate production.
It is also a widely held belief that natural gas hydrate reservoirs could be produced using largely conventional and production technologies.
Regardless of the production method, natural gas hydrate dissociation is an endothermic process, meaning it is a process that is limited by how much thermal energy is available in the vicinity. As the endothermic dissociation process proceeds and draws thermal energy from adjacent sediments, it causes them to cool. A natural consequence of dissociation of cold natural gas hydrates is the potential freezing of adjacent portions of the reservoir. Freezing of adjacent portions of the reservoir would effectively plug the well because of the very long time spans required for the frozen reservoir to naturally thaw. Addition of localized heat to thaw the frozen reservoir would also be a possible solution, but so much heat would need to be applied the economic impact would make this method prohibitive.
Natural gas hydrate reservoirs that are at pressures and/or temperatures well inside the hydrate phase stability zone (i.e. reservoirs that are very cold and/or under very high pressure) will require significant drops in pressure and/or addition of heat to initiate dissociation and will likely have limited ambient thermal energy in the surrounding sediments above and below the natural gas hydrates to support economic rates of gas production. The most desirable natural gas hydrate reservoirs are therefore those that warm and at or near the phase stability envelope. Unfortunately, it is a matter of geologic chance whether a given natural gas reservoir would meet such desirable characteristics.
Most of the natural gas hydrate research to date has focused on basic research, as well as detection and characterization of hydrate reservoirs. Extraction methods that are commercially viable and environmentally acceptable are still at an early developmental stage.
Therefore, technologies must be further developed before these additional sources of hydrocarbons become commercially-viable sources of energy.